PT2040913E - Film structure with high oxygen barrier properties and method for manufacturing such a film structure - Google Patents

Abstract

Film structure of at least five layers, two outer layers (2) made of a polyolefin on which is each time provided, on the opposite sides, a layer (4) forming a gas barrier and whereby, between both above-mentioned gas barriers (4), is provided a layer (3) made of a foamed synthetic material, whereby the outer layers (2) consist of a mixture of a polyolefin and a binder, which makes it possible to bond this polyolefin with the layer (4) forming the gas barrier.

Description

High oxygen barrier film structure and method of making such a film structure " The present invention relates to a film structure with high oxygen barrier capacity.

In the packaging industry, film structures with high oxygen barrier capacity are known.

Such film structures are applied, for example, to seal the neck of a bottle in a sealed manner using a cap, wherein the film structure is provided in the cap in the form of a film and is secured by mechanical means, or possibly through of an adhesive.

When the cap is attached to the neck of the bottle, it is sealed in a watertight manner such that the film is pushed against the neck of the bottle by the rotational movement of a screw cap or by pushing the cap on the bottle neck. It is now known that such film structures, when made of polymers, allow a certain amount of gas to pass as a function of the thickness of the film structure and the composition of the film structure.

Certain polymers, for example polyamide (PA), ethyl vinyl alcohol (EVOH) or polyvinylidene chloride (PVDC) are known for their gas barrier qualities.

However, these polymers have disadvantages, they may be hard and / or fragile and / or sensitive to moisture, and / or may have unfavorable organoleptic qualities, so that they are incompatible with various products, making them unsuitable for use as a carrier material. base and / or material to come into contact with the film in the packaging industry.

Since such a film structure must have a certain flexibility and elasticity, and a certain thickness to elastically deform under pressure and absorb the unevenness and height variations of the different parts, in other words, the neck of the bottle and the cap, relatively to each other, fragile materials can not be used.

Such a structure can not crease any of these (microchannels) and should be able to fill microchannels and cracks in the bottle neck when the structure is pushed against the bottle neck. It is further known that such thick, elastic, flexible film structures can be obtained using certain elastic and malleable polymers, such as modified polyolefins, for example satin vinyl foam (EVA), composite polymers (compounds), better known as Thermoplastic Elastomers TPE) based on polyolefins and rubber-like polymers such as styrene-ethylene-butylene-styrene (SEBS) and the like, as well as the use of thermosets (rubber). The above-mentioned structures are usually solid structures. It is also known that a malleable, elastic or thick structure can be obtained by means of production processes where a synthetic material is expanded and provided between two layers. It is the function of the foam layer to keep the structure malleable, easy to compress and robust, and lower the cost of material compared to Volkern material with the same thickness. The expansion also allows the use of cheap, known and more rigid polyolefin materials, such as 2

Polyethylene (PE), Polypropylene (PP), Polybutene (PB), mixtures of such materials or copolymers, or terpolymers of such materials.

Such polyolefin materials have an excellent moisture barrier and organoleptic qualities compared with, for example, EVA or the like.

In addition, it is known to provide a Volkern film structure with a high oxygen barrier through the coextrusion of at least three layers, in particular a first layer (A) of a modified polyolefin such as, for example, satin vinylic foam (EVA); a second layer (B) formed by a modified polyolefin, for example a polyethylene copolymer or a terpolymer having one or more functional groups, such as, for example, acrylic esters and / or maleic anhydrides and the like, wherein said second layer is a bonding layer between non-compatible polymers, such as polyolefin materials and dipolar synthetic materials, such as PA, EVOH and the like; and a third layer (C) composed of a material which forms an excellent gas barrier, such as for example EVOH or PA. The first layer (A) is designed as a contact layer with the neck of the bottle. The third layer C is not much used as a contact layer with the product since it is hard and / or brittle so that it can not seal the bottleneck well when the film is compressed. Such a non-symmetrical structure results in a problem of orientation during assembly, since each film has to be provided in the cap in a well-oriented manner. WO 99/02419 of TRI-SEAL International Inc. describes such a non-symmetrical structure in a high barrier closure coating consisting of five layers:

A first outer layer formed by a polyolefin, a gas impermeable layer, a foam layer and a second outer layer formed by a polyolefin.

This application differs from the TRI-SEAL reference in which a second barrier layer is provided on the other side of the foam layer, thereby making the film symmetrical. Also, the TRI-SEAL reference uses adhesive layers on both sides of the gas barrier layers, although this application does not have separate adhesive layers using binders in the layers to be joined.

In addition, EVOH loses its own high oxygen barrier qualities in a humid environment.

For the above reasons, a film structure with a high gas barrier, for example with EVOH, is produced symmetrically, so that layers (A) and (B) are repeated in a structure, and the structure will have the (A) (B) (C) (B) (A), wherein the structure has a specific thickness of 0.5 to 1 mm and the gas impermeable layer (C) has a thickness of about 100 micrometers. The rigidity of the overall construction is not compromised in this case, which makes this structure suitable as a sealant layer with high oxygen barrier qualities in a conventional bottle cap / bottle application. The improvement of the barrier of such a construction compared to an EVA monolayer of the same thickness is up to 400 times greater. WO 00/30846 of LAVAL HOLDINGS discloses that such a symmetrical structure with a central layer of an expanded polymer material, surrounded by two layers of a gas barrier polymer, one on each side, and two outer layers in both sides of the structure.

An advantage of such a symmetrical architecture is that the film can be used on both sides and requires no orientation before being applied. The LAVAL reference does not utilize the binders in the outer layers which provide the necessary bond between the polyolefin outer layer and the barrier layer.

A continuous increase of the oxygen barrier, which makes the EVOH layer thicker, is of no great use. The EVOH would make the film too rigid. In addition, offsetting by rendering the layer A thicker is useless since the EVOH layer C would be situated too far from the bottle neck and the oxygen inlet from the outside to the inside through the EVA layer A and of layer (B), would only increase.

Also the cost of the material would only increase with a marginal improvement of the oxygen barrier and less functionality.

In addition, EVA is not a good moisture barrier compared to PE. For the same thickness, the EVA moisture barrier is about 40 times smaller. This has an adverse effect on EVOH, whose oxygen barrier is known to decrease by a factor of 10 in case of relatively high humidity. 5

A film structure with an EVA layer of 30 microns, combined with an EVOH layer (C) of 100 microns, provides an oxygen barrier of -4.75 cc / m 2 / day at 40øC / 90% relative humidity. This is quite high. Such a construction is known as the Tekni-Plex Tri-Shield ™.

However, some applications require an even higher oxygen barrier.

This invention provides a 20 to 30-fold improvement of the oxygen barrier, comparing with known high oxygen barrier film structures suitable for sealing bottles, including Tri-Shield ™.

Other known flexible film composite structures consisting of synthetic material mostly consist of a foam layer which is provided between the outermost thin layers where a gas barrier is provided in one of the outermost thin layers in the form of a preformed sheet which is impermeable, or substantially impermeable, to gas, in particular to air and oxygen.

Such multilayer sheet having an oxygen barrier capability is usually composed of a layer of polyethylene (PE) or polyamide; a bonding layer; a layer capable of oxygen barrier; and another attachment layer, and a layer of polyethylene or polyamide. The oxygen barrier layer is, for example, a layer of polyvinylidene chloride (PVDC) or a ethyl vinyl alcohol (EVOH). The above-mentioned multilayer thin sheets are known among others under the name Saranex®. Therefore, there is a Saranex sheet on the market which is used to seal bottles, wherein the sheet has a thickness of 50 microns and is formed by a PE layer, a bonding layer, a PVDC layer, a bonding layer and a PE layer. This known sheet forms an oxygen barrier of 8 cc / m2 / day / atmosphere (ASTM D3985).

This type of sheet can be added to the expanded structure through a hot rolling process or a dry lamination process (adhesive lamination). The oxygen barrier is improved in this case, but the oxygen barrier still does not provide a substantial improvement as compared to the best embodiment of a Tri-Shield ™. The disadvantage is that by adding the Saranex-type multilayer preformed sheet or other types, by an additional lamination process, it only allows the formation of an asymmetric structure, since the additional lamination on the free side of the foam layer makes it considerably more complex and expensive film production.

Another disadvantage in adding the above-mentioned sheet is that binding such sheets to a foam layer or to one of the outermost layers, which are normally composed of polyolefin chains, does not provide sufficient mechanical strength, as a result of which the film structures obtained are disadvantageous in that the different layers will loosen after some time, so that the film structure loses its impermeability to air.

In order to prevent the different layers from loosening from the film structure, it is known to provide a bonding layer between the barrier layer to oxygen and one of the outermost layers and the foam layer, respectively.

A disadvantage in providing this bonding layer is that the thickness of the film structure increases, and that the distance between the outer surface of the film and the oxygen barrier is widened.

In fact, by widening the distance between the oxygen barrier and the outer surface of the film, the risk of air migrating through a diagonal side wall of a portion of the film increases, which makes such a film unsuitable for applications such as sealing sealing the opening of a container or the like. The present invention seeks to remedy one or more of the above-mentioned and other disadvantages.

To this end the invention relates to a film structure comprising at least five layers two outer layers composed of a polyolefin in which a layer forming a gas barrier is provided at opposite sides on opposite sides that between the aforementioned gas barriers, there is provided a layer composed of expanded synthetic material, characterized in that the outer layers consist of a mixture of a polyolefin and a binder, which bonds this layer of polyolefin with the layer forming the gas barrier without the use of a bonding layer between the polyolefin layer and the gas impermeable layer.

In addition, the foam layer may consist of a blend of a polyolefin and a binder, which bonds this polyolefin to the gas barrier layer without the use of a bonding layer between the foam layer and the barrier layer.

An advantage of a film structure according to the present invention is that, on the one hand, its structure is not too complex, on the other hand, it forms a gas barrier.

In addition, the orientation of the film provided in the lid of a bottle is not critical, since the gas barrier is provided against each of the outer layers of the film structure.

Another advantage is that the gas barrier is located relatively close (for example, less than 200 micrometers) of the other surface of the film, as a result of which, a gas flow through the diagonal side ends, for example between a gas barrier of a film and the end of an aperture to be sealed, is restricted to a minimum. The film is preferably symmetrical, so that the film has the same gas barrier capabilities in all directions, whether straight or upside down.

In addition, the outer layers and the foam layer preferably consist of a blend of polyolefin and a binder which makes it possible to attach this polyolefin to the gas barrier layer.

This preferred embodiment offers the advantage that it is not necessary to provide a separate bonding layer between the outer layer and the gas barrier, and between the gas barrier and the foam layer, so that the distance between the outer surface of the film and the gas barrier may be limited. The present invention also relates to a method for manufacturing the aforementioned film structure according to the invention, which method consists basically of making a film structure comprising at least five layers, two outer layers composed of polyolefin, in which a layer forming a gas barrier is preferred at each time on opposite sides, wherein between the above-mentioned gas barriers there is provided a layer composed of expanded synthetic material, characterized in that the material for the outer layers and the expanded synthetic layer is mixed with a binder which makes it possible to bind them to the aforementioned second layers, forming a gas barrier, and in extruding the obtained mixture.

Another advantage of the present invention is that the film structure can be manufactured relatively cheaply compared to existing film structures with a gas barrier, since the bonding layer and the adjacent polyolefin layer are extruded into a single layer, so that savings can be realized in at least one additional extrusion unit, which usually has to extrude the bonding layer.

In addition, this method also makes it possible to save on a more complicated and expensive extrusion nozzle which is suitable for the extrusion of multi-layer structures, wherein the bonding layer is to be made as an intermediate layer between the polyolefin layer and the layer of barrier layer and between the barrier layer and the foam layer.

In order to better explain the features of the present invention, the following preferred method according to the invention is given by way of example only, without being limiting in any way, as well as some preferred embodiments of a film structure according to invention, with reference to the following drawings, in which: Figure 1 shows a film structure according to the invention; Figure 2 schematically shows a method of manufacturing the film structure according to the invention; Figure 3 shows a variant of the film structure shown in Figure 1. Figure 1 represents a film structure 1 in which it basically consists of a layer 2 of polyolefin and a layer of foam 3, where the layer 4 is placed between the layers 2 and 3, which will form a gas barrier, for example, an oxygen barrier. The aforesaid polyolefin is preferably composed of polyethylene (PE), since this synthetic material is considered acceptable for applications in, for example, the food and pharmaceutical sectors.

Moreover, the PE functions as an excellent moisture barrier, which makes it possible to protect the gas barrier 4. The polyolefin layer 2 is designated as an outer layer which may come into contact with the contents of the container or the like formed by the film structure 1 or in which the film structure 1 is used as a sealing means.

According to the invention, a quantity of binders is preferably mixed in the aforementioned layers 2, and preferably also 3, enabling a good bonding of this layer 2, and preferably also 3, with the layer 4 forming a gas barrier preferably composed of ethyl-vinyl alcohol (EVOH). The amount of binder in layers 2, and preferably 3, depends on the needs and suitability of the binder in the layers referred to for the final application, i.e. the product to be packaged. Also the bond strength between layers 2 and 4 influences the amount of binders to be used. The selection of the amount of binders is made so that as little binder as possible is used, fulfilling all functional requirements therein.

A typical binder having a low concentration of functional groups is usually in a mass percentage between 5 and 20. The binder preferably belongs to a family of extrudable binders based on polyolefin having a functional group incorporated which provides the necessary bond between the polyolefins and dipolar substrates such as EVOH, polyamide (PA) and the like.

Such extrudable binders are well known in the polymer industry under the names Lotader®, Admer®, Yparex®, Orevac®, etc. The foam layer 3 preferably consists of a polyolefin such as, for example, a low density polyethylene (LDPE).

Finally, the layer 4 forming the gas barrier, preferably consists of an ethyl vinyl alcohol copolymer (EVOH) which is extruded. The polyethylene / vinyl alcohol ratio of the copolymer and the thickness of the gas barrier may then be chosen as a function of the elasticity and / or gas impermeability with respect to layer 4, where the following applies: the greater the above ratio mentioned, the more flexible the layer 4 will be and the less gas impermeability.

A blend ratio of, for example, 32/68 PE / VOH having a thickness of 50 microns per layer EVOH provides an oxygen barrier of on average 0.18 cc / m 2 day, at 40 ° C, 100% of oxygen and 90% relative humidity. A mixing ratio of, for example, 44/56 PE / VOH having a thickness of 50 micrometers per layer EVOH provides an oxygen barrier of on average 0.45 cc / m.sup.2 at 40 ° C, 100% of oxygen and 90% relative humidity. This construction provides a flexible film. However, one form of EVOH blend in the form of 70% PE / VOH or 30% 44/56 PE / VOH provides a relatively flexible film with an excellent barrier of 0.22cc / m2.day, 40ø C, 100% oxygen and 90% relative humidity with a thickness of 50 micrometers. It is evident that the thickness and the composition of the different layers 2 to 4 can be chosen in function of the requirements that are imposed in the construction of the film 1 to be made.

By varying the thickness and type of EVOH, a less flexible or more flexible film can be designed with specific barrier qualities, tailored to the specific application of the customer.

As an airtight sealant for the opening of a bottle, the outer layer 2 is preferably chosen with a thickness included between 25 and 300 Âμm (micrometers), more specifically between 150 and 200 micrometers, while for the composition of layer 4, which forms the A copolymer EVOH having from about 32 to 48 mol% of polyethylene or a blend of two EVOH copolymers is preferably based on which the mol% of both EVOH copolymers is between about 32 to 48 mole% of polyethylene. The thickness of the gas barrier may also be chosen freely, but in the above case it is preferred that it is between 5 and 100 Âμm. Figure 2 schematically shows a method according to the invention for the manufacture of the above described film structure. The above-mentioned method begins with a mixing step, wherein the different components, in particular a polyolefin 5 and a binder 6 are mixed in a desired ratio to produce an outer layer 2, wherein the at least one copolymer EVOH 7, and optionally one second copolymer EVOH 8, are mixed in a suitable ratio to produce the gas barrier layer 4 and wherein a polyolefin 9 and a binder 10 are mixed to obtain the foam layer 3.

Once the above-mentioned blends are prepared, they are extruded together in a coextrusion process to form the desired, in this case, three-layer film structure 1.

During extrusion, nitrogen gas (N2) may be injected into the mixture forming the foam layer 3 in order to expand the layer 3.

Obviously, layer 3 can also be chemically expanded, for example, by adding an amount of citric acid to the blend.

A further preferred embodiment of the film structure 1, according to the invention, is shown in figure 3.

On the one hand, in Figure 1, as mentioned above, the shown film structure 1 is composed of five layers, in particular two outer layers 2 which are identical or not, wherein a layer 4 forming a gas barrier is each time provided on opposite sides, and wherein the above-mentioned foam layer 3 is provided between the gas barriers. The advantage of the film structure 1 which is shown in figure 1 is to be provided with a gas barrier on both sides, and as a consequence, it should not be oriented prior to its application, so that when such a film structure is used as an airtight seal for containers, considerable time and expense can be saved in comparison with the case where the film structure 1 must always be turned in the right direction.

It should be noted that, in order to make better use of the aforementioned advantage, the film structure 1 is preferably symmetrical. Figure 3, on the other hand, represents another embodiment of the film structure 1, wherein between the above-mentioned outer layers 2 and the barriers to the gas 4 an oxygen-binding layer 11 has been provided.

Such oxygen-binding layer 11 offers the additional advantage that air passing through the gas barrier attaches to the oxygen-binding layer 11 and, as a consequence, no longer penetrates through the film structure 1.

In addition, by using this variant as an airtight seal for containers, the oxygen that may possibly enter the container while being sealed will be automatically removed by the oxygen-binding layer 11. It is evident that in another embodiment of the film 1 between the aforementioned outer layers 2 and the gas barriers 4, and between the barriers to the gas 4 and the foam layer 3 may each contain another connecting layer.

This then provides a nine layer film which is conventionally extruded into the different layers; however, with the advantage of being again a symmetrical structure which offers the advantage of being provided with a gas barrier on both sides and consequently should not be oriented prior to its application such that when using such a film structure as a sealant can save considerable time and expense compared to the case where the film structure 1 should always be turned in the right direction. The present invention is not in any way restricted to the above-mentioned embodiments and shown in the drawings; on the contrary, such method and film structure according to the invention can be carried out according to all types of variations, yet remain within the scope of the invention. 16

Claims (12)

A film structure comprising at least five layers, two outer layers (2) composed of a polyolefin, in which there is provided on opposite sides, a layer (4) that forms a gas barrier and wherein, between the above gas barriers (4), there is provided a layer (3) composed of an expanded synthetic material, characterized in that the outer layers (2) consist of a mixture of a polyolefin and a binder, which bonds this layer of polyolefin to the layer (4) forming the gas barrier, without the use of a bonding layer between the polyolefin layer and the gas barrier layer. Film structure according to claim 1, characterized in that the foam layer (3) consists of a mixture of a polyolefin and a binder which bonds this polyolefin to the layer (4) which forms the gas barrier, without the use of a bonding layer between the polyolefin and the gas barrier layer. Film structure according to any one of the preceding claims, characterized in that no separate bonding layer is provided between the different layers (2,3,4). A film structure according to claim 1, characterized in that between the outer layers (2) and the layers (4) forming a gas barrier, an oxygen-binding layer (11) has been placed. Film structure according to claim 1, characterized in that the layer (4) forming the gas barrier is composed of an ethyl vinyl alcohol copolymer (EVOH). Film structure according to claim 1, characterized in that the above-mentioned layer (4) forming the gas barrier has a thickness between 5 and 100 m. Method for the manufacture of a film structure according to any one of claims 1 to 6, which method consists mainly of producing a film structure comprising, at least five layers, two outer layers (2) composed of a polyolefin , in which a layer (4) forming a gas barrier is provided at each time on the opposite sides, and in that between the aforementioned gas barriers (4), there is provided a layer (3) made of a material characterized in that the base material for the layers (2) and (3) is mixed with a binder which makes it possible to bond them to the aforementioned second layers (4), and to extrude the obtained mixture. A method according to claim 7, characterized in that at least one ethyl vinyl alcohol copolymer (EVOH), or a mixture of various EVOH copolymers, is used to produce the gas barrier (4). A method according to claims 7-8, characterized in that the layers (2, 3) and the layers (4) are extruded together by coextrusion. 10. Method according to claim 7, characterized in that a polyethylene is used for the polyolefin to the outer layers (2). 2 A method according to claim 7, characterized in that a modified polyolefin is used as a binder. A method according to claim 7, characterized in that an oxygen barrier (11) is used as an additional gas barrier (4). 3